Giardia lamblia (also known as Giardia intestinalis) is a flagellated unicellular protozoan that causes acute or chronic gastrointestinal disease, giardiasis, in humans and mammals. The parasite is protected by an outer shell that allows it to survive outside the body and in the environment for long periods of time. The parasite is found in every region of the United States and throughout the world, infecting over 200 million people are infected with Giardia throughout the world. Although becoming one of the most commonly recognized causes of waterborne disease (drinking and recreational) in humans in the United States, Giardiasis is more widespread in the developing countries where infection is correlated with poor hygienic conditions, poor water quality control, and overcrowding. Also, the prevalence of diarrhea caused by G. lamblia in AIDS patients is higher than those without AIDS due to suppressed immunity in AIDS patients.
The treatment of giardiasis has changed over the past 5 years. Quinacrine (1, below) was previously used until 1998 when its manufacture was halted in the United States. The current mainstay of treatment for giardiasis is metronidazole (2, below) with reported cure rates of 80 to 95%. However, due to general toxicity and occasional drug resistance to metronidazole, an ongoing search for novel, safe, and efficacious antigiardial agents is required.
Biological evaluation of various natural products has indicated that molecules possessing a flavonoid skeleton such as geranins A (3, below) and B (4, below), kaempferol (5, below), and quercetin (6, below) exhibit antigiardial activity. Also, formononetin (7, below) and pseudobaptigenin (8, below) have been shown to possess potent antigiardial activity in vitro.

In view of these results, the present inventor developed the isoflavone derivatives of the present invention as an approach to discover a potent lead while simultaneously developing structure-activity relationships (SAR).
The isoflavones are a group of naturally occurring plant compounds having the aromatic heterocyclic skeleton of isoflavone itself (2-phenyl-4H-benzopyran-4-one). Soybeans are the most common and well known source of isoflavones, reported to contain the isoflavones, daidzin, genistin, glycitin, 6″-dadidzin-O-acetyl, 6″-O-acetyl genistin, 6″-O-malonyl daidzin, and 6″-O-malonyl genistin. Isoflavones are present in processed soy foods as well, including miso and soy sauce. Legumes, lupine, fava bean, kudzu and psoralea may also be important sources. The existence of isoflavones in Pueraria has long been known, with the roots of Pueraria containing several isoflavone compounds, such as daidzin, and puerarin. Even isoflavone itself has been isolated from Primula malacoides. 
Isoflavones are known in aglucone forms, as well as 7-acetylated and 7-substituted glycosides. Especially important isoflavones in aglucone form include daidzein, genistein, and glycitein. Especially important isoflavones in 7-glycoside form include daidzin, genistin, and glycitin. Genistein is also known to occur naturally as a 4′-glucoside (sophoricoside), and a 4′-methyl ether (biochanin A).
Isoflavones in general, and genistein in particular, have structural similarities to that of certain human estrogens, and such compounds are said to have estrogenic activity. Isoflavones are also said to have other useful biological and pharmacological activities, including antiangiogenic, antihemolytic, antiischemic, antileukemic, antimitogenic, antimutagenic, antioxidant, fungicidal, pesticidal, MAO-inhibition, phytoalexin, and tyrosine kinase inhibition activities.
The anticancer effects of genistein are of particular interest. Genistein may exert antitumor effects in part by inhibiting angiogenesis, i.e., reducing formation of vasulature and blood flow to the tumor. Its affinity to estrogenic sites in the vicinity of cancer cells may also inhibit tumor growth. As a well-known inhibitor of the enzyme tyrosine kinase, genistein may also inhibit energy and signaling pathways in tumors.
Genistein and other isoflavones are also said to be important contributors to bone health, resulting at least in part from the ability of these compounds to inhibit protein kinase activity, and thereby inhibit osteoclast cell activity. The isoflavones are especially attractive in this regard because they generally have a low toxicity relative to many other known protein kinase inhibitors.
Because of its many beneficial effects, enriched sources of genistein are marketed to consumers around the world in a wide variety of nutritional supplements. Many of the health benefits of soy products are ascribed to the presence of genistein.
More specifically, isoflavones have been linked to the following conditions and/or treatments:
Osteoporosis: Osteoporosis is a systemic skeletal disease, characterized by low bone mass and deterioration of bone tissue, with a consequent increase on bone fragility and susceptibility to fracture. See U.S. Pat. No. 6,593,310. Isoflavones have been shown to prevent postmenopausal bone loss and osteoporosis. In fact, genistein has been reported to be as active as estrogens in maintaining bone mass in ovariectomized rats. Moreover, the synthetic isoflavone derivative ipriflavone is able to reduce bone loss in various types of animal models, providing a rationale on its use in the prevention and treatment of post-menopausal and senile osteoporosis in humans. The mechanism through which isoflavones may exert the above-mentioned effects seems to depend, at least in part, on their mixed estrogen agonist-antagonist properties. An alternative hypothetical mechanism could derive from other biochem actions of isoflavones such as inhibition of enzymic activity, in particular protein kinases, or activation of an “orphan” receptor distinct from the estrogen type I receptor.
Hormone Replacement: Ovarian hormone deficiency is a major risk factor for osteoporosis in postmenopausal women. Hormone replacement therapy (HRT) is perhaps the most effective treatment, as it has been demonstrated to both reduce the rate of bone loss and risk of fracture, including hip fracture.
As used herein, the term “hormone replacement therapy” means a treatment of a human female having reduced levels of endogenous estrogen in which a mammalian estrogen is administered to the female in combination with at least one other compound, where the other compound is administered to inhibit the estrogen's tissue proliferative effects in the breast or uterus. See U.S. Pat. No. 6,326,366.
However, not all women who may benefit from HRT are willing to initiate this treatment due to fear of cancer and contraindications. Other therapeutic agents currently available are also associated with certain adverse effects. As a result, postmenopausal women are more inclined to use natural remedies such as isoflavones to alleviate postmenopausal symptoms and help reduce their risk for chronic diseases such as osteoporosis. Recent reports support the notion that certain bioactive constituents, e.g., phytoestrogens, in plants play a role in maintaining or improving skeletal health.
Cardiovascular Disease: Isoflavones, including genistein in various types of diseases such as osteoporosis, cardiovascular diseases, menopausal symptoms by accumulating evidence from mol. and cellular biol. expts., animal studies, and, to a limited extent, human clin. trials. This review suggests that phytoestrogens may potentially confer health benefits related to various diseases such as cardiovascular disorder, menopausal symptoms, and osteoporosis.
Antiproliferative Effects: Isoflavones, such as genistein, have been found to be a potent agent in both prophylaxis and treatment of cancer as well as other chronic diseases. The great interest that has focused on genistein led to the identification of numerous intracellular targets of its action in the live cell. At the molecular level, genistein inhibits the activity of ATP utilizing enzymes such as: Tyr-specific protein kinases, topoisomerase II, and enzymes involved in phosphatidylinositol turnover. Moreover, genistein can act via an estrogen receptor-mediated mechanism. At the level 1 step higher, i.e., at the cellular level, genistein induces apoptosis and differentiation in cancer cells, inhibits cell proliferation, modulates cell cycling, exerts antioxidant effects, inhibits angiogenesis, and suppresses osteoclast and lymphocyte functions. These activities make genistein a promising innovative agent in the treatment of cancer. Additionally, genistein health beneficial effects were shown in osteoporosis, cardiovascular diseases, and menopause. Genistein was also successfully used as an immunosuppressive agent both in vitro and in vivo. All these effects at the 3 biol. levels of action need varied genistein concns. and only some of them are relevant in people consuming soy-rich diet. The others would occur after purified genistein administration at higher doses. The main genistein advantage as a potential drug is its multidirectional action in the live cell and its very low toxicity.
The present inventor has discovered that the compounds of the present invention possess the benefits and usefulness of isoflavone, but are advantageous in that, among other things, have increased bioavailability and are more easily synthesized.
To more fully describe the state of the art to which this invention pertains, the following references are provided:
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